Temperature control apparatus



Aug; 1951 c. A. BLAKESLEE 2,566,053

' TEMPERATURE CONTROL APPARATUS Filed Oct. 17, 1946 2 Sheets-Sheet 1 INVENTOR.

(36mm QKBM Aug. 28, 1951 c. A. BLAKESLEE 2,566,053

TEMPERATURE CONTROL APPARATUS Filed Oct. 17, 1946 2 Sheets-Sheet 2 I N VEN TOR.

B CQM Q. BM 5.6. gm

Patented Aug. 28, 1951 UNITED STATES PATENT OFFICE CONTROL APPARATUS Clinton A. Blakeslee, Waterbury, Conn., assignor to The Bristol Company, Waterbury, Coma, a corporation of Connecticut Application October 17, 1946, Serial No. 703,835

4 Claims. (01. 236-78) This invention relates to means and method for controlling the magnitude of a condition by the application of a condition-afiecting agent in a'series of impulses whose durations are varied in response to the demand for a supply of said agent to maintain said condition with a minimum deviation from a predetermined value or magnitude. In the practice of automatic control, this form of regulation is categorically known as of the Gouy" class. In my co-pending application Serial No. 571,752, filed January 8, 1945, now abandoned, I have shown a control utilizing a cyclically operated magnetically actuated contactcr in which the durations of successive cycles of operation are varied by modifying the influence of the magnetic flux upon the contacting element in response to the deviation of the regulated magnitude from a predetermined value.

It is an object of the present invention to provide an automatic regulating system of the general class set forth in said co-pendin application, and in which the impulses characterizing the intermittent application of a condition-affecting agent shall be subject not only to the deviation of said condition from a pre-established set-point, but also to the trend of said deviation.

It is a further object to provide a regulating system of the above nature in which the relation between said impulses and the condition variations to which they are responsive shall be readily and effectively adjustable to meet a wide variety of plant and operating conditions.

In carrying out the purposes of the invention, it is proposed to utilize a plurality of magnetically actuated mercury switches of the class in which the contacting mechanism and the actuating magnet bear to each other a fixed physical relationship, rendering the action of said contactors intermittent by cyclically and steplessly varying the effective field strength of each magnet upon its associated contactor, and modifying said intermittent action by more or less independently varying the position of said contactors in response to changes in the magnitude of a regulated variable. It is further proposed to associate the contactor-controlllng instrumentalities with a condition-measuring instrument of the null or selfbalancing class in such a manner that the effective impulses derived from said contactors will be subject to variation in response both to the actual position sought or attained by the balancing mechanism of said null-type instrument, and also to the directional influence impressed upon said balancing mechanism.

In the drawings:

Fig. 1 is a diagrammatic representation of a temperature control installation embodying the principles of the invention.

Fig. 2 is an isometric view of mechanical instrumentalities combined in a manner to implement the purposes of the invention.

Figs. 3 and 4 are sectional views showing an important element of the invention in two of its characteristic operating positions.

Referring now to the drawings:

The numeral l0 designates a furnace, oven, or other enclosed space adapted to be heated by the combustion of fluid fuel admitted thereto through a burner H, and in which it is desired to maintain a predetermined constant temperature as determined by a thermocouple l2 located within the furnace, the regulation of said temperature being effected by control of the position of a valve 13 connected in a conduit l4 through which said fuel is supplied to the burner II from a source IS. The valve I3 is actuated by a reversible electric motor 20 provided with two windings and is adapted for rotation in a direction depending upon which of the respective windings is energized. Said two windings have a common point of interconnection, the free ends of said windings being connected to terminals 25 and 26 respectively, and the common point to a terminal 21.

Potentiomcter circuit and balancing mechanism The numeral 29 designates a self-balancing circuit mechanism similar to that fully disclosed and set forth and disclosed in U. S. Letters Patent No. 2,320,066 granted May 15, 1943 to F. B. Bristol, and having the following structure: A galvanometer 30 of the conventional form includes a coil 3| freely pivoted between poles N and S of a permanent magnet or the equivalent. Electrical connection is made to the coil 3| by means of resilient leads or springs 32 and 33 connected respectively to conductors 34 and 35, forming elements in an electrical network hereinafter to be described, whereby upon passage of current from one to the other of said conductors through said galvanometer coil, the latter will tend to-be rotated through a limited angle about its axis in a sense either clockwise or counterclockwise, according to the direction of the current. Carried by the galvanometer coil is a pointer 36 bearing upon its extremity a contact member 31 adapted to engage either of two stationary contacts 38 and 39, according to the sense of the deflection. The end of the coil II which is connected to the spring 33 is also connected to the pointer 35 by 3 means of aponductor 40, whereby current may pass between the conductor 34 and the pointer 36 by flowing through the galvanoineter coil 3|.

A potentiometer circuit includes a uniform slidewire 4| of arcuate curvature extended between terminals 42 and 43 and supplied with a steady unidirectional current from a battery or equivalent constant-voltage source 44, whose output may be regulated by means of an adjustable rheostat 45. Suitably enga ing the slide-wire 4| is a movable contact-arm 4B fixed to a shaft 41 coaxial with the center of curvature of the slide wire 4|, and insulated therefrom, whereby upon rotation of said shaft through a limited angle, the contact arm 45 may traverse said slide wire throughout its length, and may assume any position along said slide wire. according to the angular position at which the shaft is brought to rest. An index 48, carried by the shaft 41, and cooperating with a fixed arcuate calibrated scale 43, provides an indication of the position of said contact arm 4 with respect to the slide-wire 4|.

Rotation of the shaft 41 for the purpose of shifting the contact arm 46 along the slide-wire 4| is effected by means of a reversible electric motor 54 having two opposed windings and 52, adapted normally to be simultaneously energized and to maintain said motor stationary, and, when individually deenergized, to cause said motor to be operated in one or the other direction according to which of said windings remains energized. The shaft of the motor 50 carries a pinion 53 meshing with a gear 54 fixed to the snart 41, whereby said shaft and elements carried thereby will be angularly moved according to which of the two windings of the motor 50 is operatively eilective.

The potentiometer circuit comprising the slidewire 4|, the battery 44, the rheostat 45, and the contact arm 46 is applied to the measurement of the thermoelectromotlve force developed by the couple l2, and hence of the temperature within the enclosed space In. One element of the thermocouple is connected by means of a conductor 55 to the terminal 42 of the slide wire, and the other element to the conductor 34 leading to one side of the galvanometer coil 3|. The conductor 35, leading to the other side of the galvanometer, is flexibly or slidably connected to the contact arm 46, whereby the potential at any point along said slide-wire due to the flow of current therethrough from the battery 44, may be applied to the conductor 35 according to the deflected position of the contact arm.

According to well known principles upon which the art of potentiometric pyrometry is based, when the intensity and direction of the current in the slide-wire are suitably adjusted, the position of the contact arm 46. and therefore of the index 43, corresponding to a balance of the potentiometer network, as indicated by a zero deflection of the galvanometer pointer 36, is a measure of the temperature to which the thermocouple I! is exposed. The polarity of the thermocouple l2, as connected to the conductors 34 and 35 is made such that upon an increase of potential developed by said couple due to an increase in the temperature to which it is exposed, the unbalance current due to the excess of said emf over that derived from the slide wire will cause to pass through the galvanometer coil 3| a current tending to swing said coil in a clockwise sense, and cause the contact 31 carried by the pointer 36 to be brought into electrical engagement with the stationary contact 38. In a similar manner a decrease in temperature at the thermocouple will cause the galvanometer coil to be deflected in an opposite sense. and the con- 'tact :1 brought into engagement with the stationary contact 39. The setting of the contact by the motor 50 through the medium of a relay combination substantially identical with that set forth in said F. B. Bristol patent; and, while such combination will be briefly described, no invention thereof is herein claimed.

A relay G4 embodies an actuating magnet coil 65 and an armature 86 subject thereto. The coil 65 is fitted with a short-circuited shroud or lasplate 65', adapted to introduce a desirable timedelay in actuation of the relay, the principle of which, forming no part of the present invention, is fully set forth in said F. B.-Bristol patent. Normally engaged contacts 61 and it are adapted to be separated by the movement of the armature 68 transmitted through an insulating pad 63 l to move the contact 64 out of engagement with the contact 61 when the coil i5 is energized. Further contacts I. and II, also normally engaged, are adapted to be separated by movement of said armature transmitted through an insulating pad 12 when said coil 65 is energized. A further contact 13 is provided and adapted to be engaged by the movable contact 68 as the latter, upon energization of the coil 65, is moved out of engagement with the contact 61.

A relay 14, similar in all respects to relay 64, embodies a magnet coil 15 and an armature 16, together with normally closed contacts 11 and 18, the latter subject to actuation by said armature through an insulating pad 19 to separate said contacts, and further normally closed contacts and 8| actuated through an insulating pad 82. The coil 15 is lagged in a manner similar to the coil 65, and all the elements of the relay 14 are proportioned and adjusted to. give a performance substantially identical with that of the relay S4 with respect to sequential actuation of contact elements. A further contact 83 is provided and adapted to be engaged by the movable con-' tact 18 as the latter, upon energization of the coil 15, is moved out of engagement with the contact TI.

'l'he galvanometer contact 38 is connected through a conductor 34 to one terminal of the coil 65, and the free terminal of that coil by means of a conductor 85 to the contact 10. The contact H is connected by means of a conductor 86 to one terminal of a small battery or other suitable source of unidirectional electromotive force 81, and the other terminal of said source to the conductor 34. The galvanometer contact 39 is connected through a conductor 88 to one terminal of coil 15, and the free terminal of that coil by means of a conductor 89, contacts 80, 8|, and a conductor 90, to one terminal of a D.-C. source BI, and the other terminal of said source to the conductor 34. It will be seen that, upon deflection of the galvanometer pointer 36 sufficiently for the contact 31 to engage the contact 38, a circuit will be completed from one side of the source 81 through the normally closed contacts IO-ll, the magnet winding 65, the contacts 38 and 31, and the galvanometer coil 3| to the conductor 34, and thence to the otherside of said source. Similarly, upon deflection of the pointer to a position of engagement, with the contact 39, a. circuit will be formed from one side of the source 9| through contacts 808l, magnet coil 75, contacts 39 and 31, the galvanometer coil 5 I, and the conductor I4 back to the other side of said source.

The polarities of the several sources of electromotive force in the network described are so selected that upon deflection of th e galvanometer in either direction by current derived from said network flowing in the coil 3 I, the supplementary current in said coil derived from the corresponding one of the sources 81 or will be in such a direction as to tend to deflect the galvanometer in the same direction with added intensity, thus supplementing the original directive effort, and tending to amplify the pressure exerted between the movable contact 3'! and the stationary contact engaged thereby. The arrangement of the mechanism and the connections of the potentiometer network are such that upon energization of the winding alone of the reversible motor 50 the consequent movement of the contact arm 40 along the slide-wire 4i will be toward the terminal 42 and will tend to reduce the potential between the conductors 55 and 35; and when the winding 52 is energized alone, the movement of the arm 46 will be toward the terminal 43 and will tend to increase said potential.

One terminal of each of the windings 5| and 52 of the reversible motor 50 is connected to a common conductor 95 representing one side of an electric power supply. The free terminal of the winding 5| is connected by means of a conductor 96 to the contact 61 in the relay 64, and the cooperating contact 68 to a conductor 91, forming the other side of said supply. The free terminal of the motor winding 52 is connected by means of a conductor 98 to the contact TI, and the coacting contact I0 to the conductor 91. Thus, it will be seen that with the contact pairs 61--68 and IT-18 in their normally closed positions, both windings of the motor 50 will be simultaneously energized, tending to stall the motor, and that with one of these contact pairs opened while the other remains closed, the motor will be energized for rotation in a corresponding direction as hereinbefore stated. The operation of the device, as thus far set forth, may be briefly stated as follows: If the position of the contact arm 46 with respect to the slide-wire 4i is such that there exists a condition of balance between the potential developed by the couple I2 and that derived from the potentiometer network, the galvanometer will stand in its undeiiected position, with the contact 31 out of engagement with either of the cooperating contacts 38 and 39; and relays 65 and will be de-energized, and their respective contact pairs 61-68 and I1'I6 closed, causing both windings of the motor 50 to be energized, and the motor consequently to remain at rest. Upon a deviation of the thermocouple potential from that derived from the slide-wire,

the unbalanced condition will cause a current to flow in the galvanometer coil 3| deflecting it in a sense to close a corresponding contact, and to energize which ever one of the relays 64 and 65 will close the motor 50 to be operated in a direction to move the contact arm 46 to a position on th slide-wire where a condition of balance will be restored. For purposes of discussion it may be assumed that upon an increase in the temperature measured by the thermocouple I2 the contacts of the galvanometer 30 will be actuated in a sense to energize the coil 65 of the relay 64, with a consequent contact action causing the motor 50 to rotate the shaft 41 and parts carried thereby in a clockwise sense as seen in the drawing, and vice versa. This balancing action is characteristic of many forms of null-type instruments and. as it forms no part of the present invention, and, moreover, is fully set forth in the aforementioned F. B. Bristol Patent No. 2,320,066, need not here be further elucidated. The function of the current flowing throughthe galvanometer coil 3| from the sources 81 and II through the contact pairs IO-II and in amplifying the pressure of the galvanometer contacts, together with the timing characteristic introduced by the lagging coils or shrouds on the relay windings and I5 is also identical with that shown in said patent, and need not here be explained in further detail.

Relays and trend-responsive mechanism Control of the valve I! in response to deflections of the shaft 41, and modification of said control in response to the trend of said deflections is efiected by instrumentalities comprising in combination the following elements: Included in a control assembly IOI are two circuit-closing relays I02- and I03, and a mechanically locking position assumed consequent to energization of 7 either of said coils and to retain it in that position until the other of said coils is energized. The relay I04 is further provided with two pairs of coacting contacts H0 and III, the former being electrically engaged and locked in that position after energization of the coil I05, while the latter remains open, and the respective conditions of said contacts beinginterchanged after energization of the coil I06.

The mechanical instrumentalities whereby the hereinbefore described relays may be rendered effective to control the valve I3 in response both to variations in the temperature of the thermocouple I2 and to the trend of said variations will best be understood by reference to Fig. 2, taken in conjunction with Fig. 1 of the drawings. In addition to said relays, there is included in the control assembly IIII a mounting base 5, to which may be secured the self-balancing circuit mechanism 29 in addition to further devices presently to be described. Carried by the shaft 41 of said self-balancing mechanism is a cam member H6, and having a spirally conformed profile whereby its eifective radius at any selected fixed position will be varied with angular displacement of said shaft. Mounted for adjustable positioning through a limited angle about an axis A concentric with the shaft 41 is an arm III carrying a pointer or index.l l6 adapted to cooperate with the graduated scale 46 in providing an indication of the adjusted position of said arm. Integral with said arm is a bearing portion having journalled thereon for deflection through a limited angle about an axis B parallel to, and movable about, the axis A, a lever arm I I6 substantially tangential to the contour of the cam member 6 and terminating in a cam-follower element I20 adapted to engage the periphery of saidcam member, whereby to deflect said arm about the axis B through an angle dependent upon the angular position about the axis A of the arm I" in relation to the shaft 41 and the cam member 6 carried thereby. Attached to the arm II 3, and deflectable therewith, is a downwardly extending arm I2I carrying a radially adjustable pin I22, and preferably provided with a; graduated scale portion I23 whereby the radial distance of said pin from the axis B may readily be determined. I

Pivotally mounted for limited angular deflection about horizontally displaced'axes C and D, both parallel to the axis A, are vertically disposed arms I25 and I26, each adapted to carry an electrical circuit-controlling member of a. type presently to be described. The arm I25 is provided with an upwardly-extending part I21 having a substantially radial edge adapted to be engaged by the pin I22, whereby said arm will be deflected about the axis C as the arm I2I is deflected about the axis B, the angular displacement of the former arm with respect to'that of the latter being dependent upon the adjusted position of the pin I22 in relation to the-scale I23. Positive engagement of the edge of the part I21 with the pin I22 is assured by a tension spring member I28 extended between suitably positioned abutments positioned respectively on said extended part I21 and on said arm I2I.

A screw I30 passing through a pivoted abutment on the arm I26 and threadedly engaging a pivoted abutment on the arm I25, and encircled by a compression spring I33 bearing against said abutments, serves to maintain said arms in substantial parallelism while at the same time permitting angular adjustment of one of said arms with respect to the other.

Attached to the arms I25 and I26, and movable therewith are circuit-controlling devices or contact elements I35 and I36, in the form of magnetically actuated mercury switches of the type fully set forth and described in U. S. Letters Patent No. 2,085,316, granted to K. Hunciker, June 29, 1937. Such a contactor comprises an evacuated glass envelope having in its lower portion a small pool of conducting liquid, such as mercury, and two contact elements, one stationary, and the other movable and spring supported, extending downward into said pool to make electrical contact therewith. The latter contactor is provided with a ferromagnetic armature subject to the influence of a magnet exterior to said envelope, whereby, by varying the effective field strength reaching the armature, said contact element may be caused to dip into, or spring out of, the mercury pool, thus completing or interrupting the electrical circuit between said contact elements. The conventional method of actuating contactors of this type is by either moving a permanent magnet in relation thereto, or by varying the excitation of an electromagnet having one of its poles juxtaposed to said armature. An operating performance better suited to the purposes of the present invention is obtained by mounting a magnetically-actuated contactor and a permanent magnet in fixed relationship, and varying the effective field strength of the latter upon the former by the expedient of more or less interposing between the magnet and the armature a ferromagnetic shield, whereby to divert or shunt more or less of the flux of the magnet, and thus cause the field effective upon the armature to be varied above and below a predetermined minimum value necessary to actuate the same. The operation of a magneticallyactuated mercury switch by diversion of more or less of the flux from a juxtaposed permanent magnet is set forth in U. S. Letters Patent No.

l 1940, and also in my hereinbefore mentioned eopending application Serial No. 571,752.

In Figs. 3 and 4 is shown the magnetically actuated contactor I35 with its component elements in their two respective characteristic operating positions. Sealed through the walls of an evacuated glass envelope I and having terminals extip in a pool or globule of mercury I lying in the III lowest part of the envelope I40, while the movable contact element I42 is normally maintained by the influence of the resilient spring member I43 in a position out of engagement with the surface of said pool, as indicated in Fig. 3. Secured to a bracket part I41 integral with, and projecting outward from, the arm I25, is a small permanent magnet I46, separated from the outer surface of the envelope I40 by an air gap, and so disposed with respect to the elements therein that its field, acting directly upon said armature, will be sufficient to deflect the same and its supporting contact element I42 against the influence of the spring member I43 from the normal position of non-engagement with the pool I45 to a position where said contact element will touch the mercury, completing an electrical circuit between the external terminals.

The contactor I36, mounted upon the movable arm I26, is identical in all respects with the contactor I35, and is adapted to be similarly responsive to a permanent magnet I49 secured to a bracket part I50 integral with the arm I26. The mountings of said contactors and their respectively associated magnets is made such that the interposed air gaps embrace a common plane perpendicular to the axes C and D about which said contactors and magnets are movable with angular displacements of their respective supporting arms I25 and I26.

Carried by a shaft I54, journalled for continuous rotation about an axis parallel to the axes C and D, and substantially midway between the contactors I35 and I36, is a spirally conformed plate I of ferromagnetic material adapted to pass freely through the air gaps between said contactors and their associated magnets. The structure, material and conformation of the plate I55 are made such that when the portion of greatest radius is interposed in the air gap between either of the contactors and its associated magnet, as indicated in Fig. 3, suflicient of the flux therefrom will be diverted or shunted through the mass of the plate as eiIectually to short circuit" the magnet and provide a barrier, so that the armature of the contactor will be released, and the movable contact member permitted under the influence of its resilient support to deflect to its open-circuit position. When the portion of the plate I55 having its minimum radius is toward the air gap, the diversion of flux will be insuflicient materially to weaken the efiective strength of the magnet, so that the armature will be attracted, as indicated in Fig. 4, and the movable contact moved to its closed-circuit" position. Thus,-if the plate I55 be rotated about its axis. the electrical circuits of the contactors I35 and I36 will be intermittently, alternately, and inde pendently opened and closed.

The mobility of the contactors I35 and I36 2,214,159, granted to F. B. Bristol September 10. 76 about the axes C and D respectively imparts to them a freedom of displacement a comdeflection of the other, of said arms, and vice versa.

Mounted upon the base H6 is a motor device I 66 having a shaft I 6| extending forward parallel to the shaft I 66 and adapted for continuous rotation at a speed of the order of 12 revolutions per minute. Supported upon an insulating. post I66 carried by the base I I6 is a contact assembly comprising a deflectable resilient arm I66 having a contact member I61 adapted to engagesimultaneously two mutually insulated contact members I66 and I66 carried by arms I16 and "I respectively, also supported upon the post I66. Carried by the shaft I 6I is an eccentric cam member I12 adapted to engage the resilient arm I66, and deflect it to an extent that the contact member I61 is brought into electrical engagement with the contacts I66 and I66 for a portion of each revolution of said shaft.

Carried on the forward extremity of the shaft III is a gear I16 meshing with a pinion member I16 on the shaft I66. Said gear members are preferably made removable, or otherwise adapted to convenient changing of the velocity ratio between the shafts I 6| and I 66. While this ratio is subject to variation in accordance with the nature of the plant under regulation, it has been found that a large proportion of control requirements are met when the relative dimensions of the gear and pinion are such that the shaft I 66, and the barrier-plate 155 carried thereby make five revolutions for each revolution of the shaft I 6| the cam member I12 rotating with said last-named shaft being proportioned and adjusted with respect to the contact system actuated thereby so that the contact I61 is in engagement with the contacts I66 and I66 for a time interval representing one complete revolution of the plate I66.

Electrical connections The combined elements of the control assembly I6I are operatively associated with those of the s lf-balancing circuit mechanism 26, and with the valve motor 26, by means of the following electrical connections shown in Fig. l: The contact spring I66, one side of each of the contacts IIIl-III, and of the coils I66-J66, in the locking relay I66, together with the common terminal 21 of the motor 26, are all connected to the line conductor 66. One side of each of the mercury contactors I 66I66 and one side of each of the contacts in the relays I62I66 are connected to the line conductor 61. The contact 16 of the potentiometer-balancing relay 66 is connected to the free terminal of the locking relay coil I66 by means of a conductor I66; and the contact 66 of the relay 16 to the free terminal of the coil I 66 by means of a conductor I 6|. The free terminal of the contactor I36 is connected to one side of the winding of relay I62 by means of a conductor I62, and the other side of said winding by means of a conductor I 66 to 1 the free side oi contact III and to contact arm I16. Similarly. the free terminal of the contactor I66 is connected to one side of the wind- In: of relay I66 by means of a conductor I66, and the other side of said winding by means of a conductor I66 to the free side of contact II I and to contact arm "I. The free contacts 01 the relays I62 and I 66 are connected by means of conductors I66 and I61 to the terminals 26 and 26 respectively of the valve motor 26. whereby closing of the contacts of relay I62 will apply the line voltage existing between conductors 66 and 61 to the motor to operate the same in a sense to close the valve I6, and closing of the contacts of relay I66 will apply said voltage to the motor to open said valve. 7

Operation of control mechanism (General) The manner in which the shaft 61 and parts carried thereby, including the index or pointer 66 and also the cam member II6 are caused to assume angular positions representative of temperatures to which the thermocouple I2 is expomd has already been made clear; and the manner in which the position of said cam member is coordinated with the trend of temperature change to regulate said temperature will now be explained. By adjustment of the screw I66, the relative positioning of the arms I26 and I26, with the contactors I66 and I66 carried thereby, is made such that when the indication of the pointer 66 coincides with the setting of the index I I6 on the scale 66, the angular position of the arm II6 about the axis B, and also of the arm I2I will be such that said two contactors, displaceable thereby, will be alternately'and equally influenced by the barrier plate I66 in its continuous rotation. Thus, in each cycle determined by the rotation of said plate, the "clwed-circuit" intervals of said respective contactors will be of equal duration, as also will the open-circuit intervals. The conductors I62 and 866 will thus be alternately, and for equal time intervals, connected to the line conductor 61.

Operation (Deviation-responsive characteristic) Since the control system has a dual characteristic, responsive to both the deviation of the measured variable from the control point and the trend of such deviation, its action will best be understood by considering the nature of suchresponses more or less independently. with this obiect in view, it ma first be assumed that the contacts I61-I66I66 are allowed to remain in mutual engagement, as might be done by releasing the cam I12 from the shaft 16! and locking it in the position where said contacts are maintained in a closed-circuit condition. Under these conditions, it will be seen that the contacts I I 6 and III of the relay I66 are bridged through conductors I66-I66, both connected to the line conductor 66. Thus, as the conductors I 62I66 are altematelv connected to the line conductor 61 through the intermittent action of the mercury contactors, the relays 162-4 66 will be alternately energized, imparting to the motor 26 reversing action, whereby the valve I 6 will oscillate through a small range. Since, under the hereinbefore stated condition of agreement between the measured and set temperature values, the alternate energization intervals of the relays I 62 and I63 are mutually equal, the mean position of the valve I6 will remain unchanged, and the average rate of fuel admission to the furnace I6 will be constant.

Assuming, now, that the temperature at the thermocouple I2 should rise. with a consequent rotation of the shaft 41 in a clockwise sense, it will be seen that, due to the eccentric conformation of the cam'member IIB rotating with said shaft, the arms I13 and I22 will be angularly displaced about their common axis B, and the latter arm, acting through the pin I22 upon the extended portion I21 of the arm I25, (which arm is operatively connected to the arm I26 through the interconnecting screw I30) will cause the arms I25 and I25 both to be deflected in a clockwise sense about their respective axes. Thus, the mercury contactor I35, together with its associated magnet I45. will be swung to a position more remote from the center of the plate I55, and consequently will be for a shorter period in each revolution subject to the shielding influence of said plate, while the cycle of operation of the contactor 838 will be subject to change in the opposite sense. Thus, the impulses of the relay I02, derived from the contactor I35 will be lengthened, and those of the relay I03 correspondingly shortened, with the result that the "closing imnulses upon the valve I3 are increased, while the opening impulses are decreased, with a resultant action tending to close said valve, lessen the fuel supply, and lower the temperature in the heated space. Conversely, it will be obvious that a lowering of temperature at the thermocouple I2, acting through the potentiometer mechanism 29 and the cam member I I6, will be responsible for a displacement of the mercury contactors to positions with respect to the rotating barrier plate I55 where the net result of their alternate impulses will be to open the valve I3 and increase the fuel supply.

Operation (Trend-responsive characteristic) The regulation, as above described, while responsive only to the direction of deviation of the regulated variable from the control point, would in itself tend to maintain the temperature at the predetermined desired value, but would be slow of response and would tend to set up an oscillatory condition whose elimination is one of the objects of the present invention. In order to obtain an understanding of the response of the control system to the trend of change in the regulated variable, consideration may now be given to the performance obtained if the cam I12 were to be locked in a position where the contacts I61I 60-4 69 remain out of engagement, all other elements of the control operating in a normal manner. Since the contacts H and III of the relay I04 are no longer bridged by said camactuated contacts, circuits will be completed between the conductors I82-I04 to the line conductor 91 only as one or other of said relay contacts is closed by action of the relay I04 in response to energization of one or other of its actuating windings I05 and I06. Since these windings have each one side connected to the line conductor 95, and their other sides alternatively through the conductors I80 and IBI and the contact systems of the relays 54 and 14 respectively to the line conductor 91, it follows that the position assumed by the armature of the relay I04 will depend upon which of the contact pairs 68-13 or 18-83 was last engaged, which, in turn, will depend upon which of the relay coils 6515 was last energized. Thus, the contacts H0 or III in the relay I04 will assume a position dependent upon the sense of the latest deflection of the galvanometer coil 3!. as subject to the direc- 12 tion or trend of temperature change at the thermocouple I2, and will retain that position until there occurs a reversal in the trend of temperature change.

If it be assumed that the direction or trend of temperature change is upward, the relay 54 of the potentiometer-balancing mechanism will be active, and each timethe coil 65 is energized, the consequent contact actions will include intermittent closures of the contact elements 58-43, so that the coil I05 of the relay I04 will be energized, causing said relay upon the first such energization to assume the position shown in the drawing, with the contacts IIO closed and the contacts III open, and so to remain until such time as the coil I06 may be energized. With the contacts I51-I 00 separated, and the parallel path thereby to the motor 20 in a sense progressively to close the valve I3 and reduce the fuel supply at a rate of reduction dependent upon the magni-- tude of the required correction.

Should the trend of temperature change become downward. this will immediately be reflected in a counter-clockwise deflection of the galvanometer coil 3|, a consequent engagement of the contacts 31-39, energization of the relay coil 15. and a momentary closing of the contacts 18-03, with resultant energizationoi the relay coil I05, whereupon the armature of the relay I04 will at once move to, and lock into, a position where the contacts IIO are opened and the contacts III closed. Under this condition only opening" impulses can be imparted to the fuel valve I3, so that an increase in fuel supp will be initiated immediately upon the temperature change taking a downward trend, and without waiting for the regulated temperature to fall below the value at which the index IIB may be set.

Summary of operation Both the above-discussed conditions of performance have been based on the assumption of the cam I12 remaining inactive to affect the relation between the contact I51 with its two mating contacts I68--I69-; and it will be seen that, so long as a closed-circuit condition exists among these contacts, regulation will beleil'ected solely in response to deviation oi. the regulated value from the control point, and whilean open-circuit condition exists, regulation will depend primarily upon the trend of said deviation. The intermittent closing and opening of said contacts, due to action of the cam member I12 will cause the performance of the control to alternate between the two characteristics; and, with the 5/1 ratio between the speeds of the shafts I54 and I6 I there will be obtained four successive adjustments of the fuel valve in response to the anticipatory" characteristic introduced by the trend-sensitive elements of the combination. followed by a single adjustment in direct response to the actual deviation, thus positively stabilizing the control point and eliminating any tendency to drift" or to develop a reversed action subsequent to extremely sudden changes in the value of the measured variable or in the setting of the control point.

Manual alteration of the position of the pin I22 radial'y with respect to the arm I will vary the angle of displacement of the arms I25 and I26 about their respective axes for a given displacement of the shaft 41, thus providing an adjustment of the throttling range of the control. The screw I30, acting in opposition to the influence of the compression spring I33, to determine the angle between the arms I25 and I26, makes it possible to regulate the relative durations of closed and open intervals for the mercury contactors I35 and I36, and, if desired, by spreading the contactors suiliciently far that in a neutral position neither of them is influenced by the plate I55, to establish a dead zone in which no regulating action will take place.

The terms and expressions which I have employed are used as terms of description and not of limitation, and I have no intention, in the use of such terms and expressions, of excluding any' equivalents of thefeatures shown and described or portions thereof, but recognize that various modifications are possible within the scope of the invention claimed.

I claim:

1. In a condition-regulating system, a measuring member adapted to assume a position representative of the magnitude of a condition to be regulated, a member movable in response to changes in said condition and thereby adapted to control the position of said measuring member,

a pair of switch means for controlling a condition-affecting agent in different senses respectively, means subject to the position of said measuring member for actuating the respective switch means in alternate impulses of durations dependent upon said magnitude, and means subject to said movable member and independent of the position of said measuring member for modifying the relative activity of said respective switch means.

2. In a device for controling a variable condition, means for producing an electrical effect proportional to the magnitude of saidcondition, and opposing said effect to a predetermined electrical effect, a movable member adapted to be displaced in a direction dependent upon the difference between said opposed effects, a measuring member adapted to be positioned under the influence of said movable member and to assume a position representative of said magnitude, a pair of switch means for controling a'condition-afiecting agent in different senses respectively, means for actuating the respective switch means in alternate impulses of durations dependent upon the position of said measuring member, and means for superimposing on said switch means an in- 50 3. In a condition-regulating system, a measuring member adapted to assume a position representative of the magnitude of a condition to be regulated, a member movable in response to changes in said condition and thereby adapted to control the position of said measuring member, a pair of switch means for controlin a conditionaffecting agent in difierent senses respectively, means subject to the position of said measuring member for actuating the respective switch means in alternate impulses of durations dependent upon said magnitude, means subject to said movable member and independent of the position of said measuring member for inhibiting operation of one of said switch means when said movable member is in one position and for inhibiting operation of'the other of said switch means when said movable member is in another position, and means for periodically inhibiting the action of said inhibiting means.

4. In a condition-regulating system, a measuring member adapted to assume a position representative of the magnitude of a condition to be regulated, a member movable in response to changes in said condition and thereby adapted to control the position of said measuring, member, a pair of switches for controling a conditionafiecting agent, impulse transmitting means controlled by said measuring means for transmitting cyclical impulses of durations corresponding to magnitudes of said condition, other' impulse transmitting means for transmitting cyclical impulses of durations complemental to those of the first mentioned transmitting means, connections from the respective transmitting means to the respective switches, means subject to said movable member and independent of said measuring means for establishing com-- munication between one of said switches and the corresponding transmitting means when said movable member is in one position while concurrently disrupting communication between the other switch and its transmitting means and for establishing communication between said other switch and transmitting means when said movable member is in another position while concurrently disrupting communication between the first mentioned switch and transmitting means,

and means for periodically establishing communication concurrently between both said switches and the corresponding transmitting means regardless of the position of said movable member.

CLINTON A. BLAKESLEE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,119,061 Stein et al. May 31. 1938 2,209,566 Hornung July 30, 1940 

